Note: this creates a new namespace and lauches bash in that context. It then umounts the USB filesystem and then unhides the USB subsystem. Note that this doesn't unmount USB for the host, or any existing guests, but the umount is necessary for the setattr to take effect.

To make this persist for a specific guest, add the following to `/etc/vservers/<guest>/scripts/pre-start`:

Note this is a bit of brute force. It enables all guests to see USB (assuming they have the right `fstab` entry, below, and doesn't turn it off. If you want to be more fancy, you can probably rehide the USB when the guest is shut down. However, this will break if you have more than once guest using USB